Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$243.28	11.702%	$271.7486	$271.75	$271.75	$271.70
Purchase #2	$25.98	5.825%	$27.4933	$27.49	$27.50	$27.50
Purchase #3	$86.50	7.432%	$92.9287	$92.93	$92.95	$92.90
Purchase #4	$97.81	4.177%	$101.8955	$101.90	$101.90	$101.90
Purchase #5	$228.73	12.801%	$258.0097	$258.01	$258.00	$258.00
Purchase #6	$143.27	13.256%	$162.2619	$162.26	$162.25	$162.30
Purchase #7	$138.76	3.461%	$143.5625	$143.56	$143.55	$143.60
7 purchase totals =	$964.33		$1,057.9002	$1,057.90	$1,057.90	$1,057.90